The present invention relates generally to the field of circuit interrupting devices. More particularly, the invention relates to a technique for enhancing interruption through such a device by gas dynamically forcing expansion of an arc by means of surface ablation of a source element.
Various circuit interrupters are currently available and have been developed for interrupting a current carrying path between a source of electrical power and a load. In general, such devices include one or moveable contacts and a mating contact. The contacts are joined to complete a current carrying path through the device during normal operation. The contacts may be separated, such as in response to overcurrent conditions, loss of phase, ground faults, or other unwanted events. Upon displacement of the moveable contact from its mating contact, an arc develops which is caused to expand and migrate towards a dissipating structure, such as a splitter plate stack. In general, a goal in such devices is to interrupt current as quickly as possible, to limit let-through energy and thereby to provide enhanced protection to downstream circuitry.
Approaches to rapid extinction of arcs circuit interrupters have taken various strategies. For example, devices have been proposed which cause rapid expansion of an arc by movement of the moveable contact or by movement of both mating contacts. The expansion of the arc may also be driven by electromagnetic means, such as a core structure which develops a magnetic field during interruption. While such approaches are useful in enhancing performance, further improvement is needed in circuit interrupters. There is, at present, a need for additional techniques to cause higher voltage investment in an expanding arc, and to force a further expansion of the arc to extinguish the arc even more quickly, and thereby to further limit let-through energy.
The present invention provides a novel technique for interrupting current through a circuit interrupter designed to respond to Such needs. The approach may be implemented in a variety of device configurations, including in devices which develop a single arc and in those which develop a pair of arcs by displacement of a conductive bridge or spanner. In accordance with aspects of the technique, the arc developed during circuit interruption is driven in a desired direction, typically toward a dissipating structure, such as a splitter plate stack. The arc may be driven in a variety of manners, such as electromagnetically by a field developed around a circuit interruption initiator. A source element undergoes surface ablation during the interruption event to provide a flow of gas which is directed toward the arc. The gas opposes the direction of migration of the arc, forcing expansion of the arc and more rapid extinction.
In a preferred embodiment described, the source element is provided in a second current carrying path which is parallel to the primary current carrying path in which the moveable contact is situated. The primary current carrying path supports all current through the device during normal operation, with no current through the parallel current path. During circuit interruption, current is partially directed through the parallel path including the source element, causing heating and surface ablation of the source element. Gas released by the surface ablation is directed toward the arc, which is forced to migrate in the direction of the source, element. The source element may be a material which transitions from a first resistance level to a second, higher resistance level due to heating, thereby protecting the source element from damage during operation. Where a conductive spanner or bridge is provided, source elements may be provided on either side of the spanner to direct flow of gas in the direction of a pair of arcs, both expanding and migrating toward dissipating structures on either side of the spanner.